In oil and gas exploration industries, seismic survey is a technique for determining the detailed geographic structure underlying a particular area by propagating acoustic shock waves into the strata and detecting and measuring the reflected seismic wave signal. The seismic survey technology is now recognized as a crucial area for oil and gas exploration and production industries in order to increase capital efficiency, minimize the risks for capital investment, eliminate the dry holes and increase oil production throughput.
Fiber optic based seismic survey sensing technology improves penetration through salt domes by reaching beyond 10,000 feet in depth with a resolution of less than 50 feet. This improved performance helps to discover additional new oil or gas reserves.
The core components in a fiber optic seismic system are the low phase noise laser sources and sensitive seismic fiber optic sensors (e.g., accelerometers, hydrophones or geophones) based on interferometric principles. The laser sources need to show not only low phase noise, but also low sensitivity to external vibration disturbance due to harsh environment.
Conventional high power telecom grade diode lasers exhibit narrow linewidth and low sensitivity to vibrations due to its small size. These characteristics make them suitable for use as coherent light source for interferometer-based applications. But they exhibit high phase noise in the seismic sensors working frequency range, typically 1-1000 Hz. Other types of lasers such as optical fiber lasers exhibit low phase noise but their phase noise increases dramatically in the field environment due to the sensitivity of the optical fiber (fiber length to be exact) to acoustic or mechanical vibrations (causing jitter and wavelength drift), which makes their use difficult without isolating the optical fiber lasers from harsh environmental disturbances.
These technical challenges and difficulties may hinder further development of fiber optic seismic sensing systems. In order to fulfill the need of fiber optic seismic sensing functions, vibration insensitive low phase noise laser sources are needed.
Other applications, such as precision spectroscopic measurements, hydrophone sensors, LIDAR, RF signal generation, coherent communications may also require low phase noise laser sources.
Furthermore, due to the high wavelength density nature of fiber optic seismic sensing systems, there is still a need to design and manufacture laser sources capable of both wavelength tuning and self-calibration to provide sufficient wavelength accuracy.